Cyclopentadiene is present to the extent of about 15% in the naphtha cracker C.sub.5 by-products stream from ethylene plants. One way to dispose of the C.sub.5 by-products stream is to use it as a fuel stock, however, a better use is as a source of petrochemicals. The most sought-after component of the C.sub.5 by-products stream is isoprene, which is also present at about 15% level. With the soaring price of natural rubber, pressure is mounting to expand synthetic polyisoprene production. For every pound of extract isoprene capacity that comes on stream, there will be a pound of cyclopentadiene. Thus, it stands to reason that with the sharp rise in the cost of crude oil, ethylene producers will have a strong incentive to find the most profitable uses for the by-products. In this context, cyclopentadiene is high on the list since its removal from the C.sub.5 stream is easily accomplished at the first step of the C.sub.5 purification process.
This invention pertains to reactions which involve cyclopentadiene in the formation of hydroxybenzylcyclopentadienes and derivatives thereof which are useful as antioxidants for stabilizing polymeric materials, and to processes for making such antioxidants.
The art of stabilizing polymeric materials is both complex and unpredictable. Ordinarily, the stabilizing agent is physically combined with the polymer thereby prolonging its useful life in the hostile degradative environment. In such cases, the stabilizing agent is generally free to slowly migrate within the composition and to the surface thereof. This presents a problem where the polymer is contacted by fluids which can extract the stabilizing agent. Furthermore, some stabilizing agents are very volatile and can change from a solid to a vapor at relatively low temperatures. Exposure of compositions containing such heat sensitive stabilizing agents will result in vaporization of the stabilizer and its eventual diffusion from the polymer. Whether the stabilizer is lost by fluid extraction or vaporization, or by any other means for that matter, the end result is that the polymer will become vulnerable to attack by degradative forces.
It is therefore desirable to have antioxidants which can be bound into the polymeric material to prevent its extraction, as by leaching, vaporization, or in any other similar fashion. The antioxidants herein have the capacity of being chemically bound into the polymeric material since they contain at least one double bond which can participate in an addition reaction with other polymeric materials during polymerization of the monomers or thereafter during curing when crosslinking would take place and finally during processing when a Diels-Alder reaction would bind the antioxidant to an unsaturated polymer such as cis-polybutadiene.